The present invention relates to an air filter housing with an intake air filter for the mixture formation device of an internal combustion engine, especially for the carburetor of a two or four stroke engine. Formed in the filter housing is a clean air receiving chamber that is delimited by a filter element. An intake opening opens into the clean air receiving chamber for establishing communication of the intake air filter to the intake channel of the mixture formation device. A deflection bowl covers the intake opening in a hood-like manner. Provided in the peripheral wall of the deflection bowl is a communicating window that is disposed transverse to the intake channel and serves for the flow communication with the clean air receiving chamber.
U.S. Pat. No. 4,600,416 discloses an intake air filter where the filter housing is essentially composed of two housing halves. The lower portion of the filter housing forms a baffle or deflection bowl that spans the intake opening in the filter housing in an essentially hood-like manner; provided in the peripheral wall of the deflection bowl is a communicating window to the clean air receiving chamber of the intake air filter.
This known intake air filter was intended to keep the fuel portion of the intake air that pulsates back away from the filter element, so that the filter element could reliably fulfill its function over a long period of operation. However, it was discovered in practice that under unfavorable operating conditions, intake air saturated with fuel could flow back into the clean air receiving chamber of the air filter via the communicating window, whereby this fuel becomes deposited in the air filter element. This increases the resistance to flow of the filter surface, bringing about a loss in efficiency of the associated internal combustion engine. In addition, the filter element becomes dirty more quickly, and must be cleaned more frequently.
It is therefore an object of the present invention to improve an intake air filter of the aforementioned general type in such a way that even under unfavorable operating conditions entry of mixture-saturated intake air into the clean air receiving chamber of the air filter is prevented.